Atherosclerosis or vascular disease is the leading cause of death in the world today. It is a disease of the arteries whereby deposits (plaque) build up over time in the walls of the arteries, restricting oxygenated blood flow to vital organs such as the heart, brain and other bodily tissue. A number of medical procedures have been developed to treat vascular disease such as Coronary Artery By-Pass Grafting (CABG) and Percutaneous Balloon Angioplasty (PTCA) and Stenting. These procedures are intended to restore normal flow through the arteries.
In the case of CABG, the saphenous vein is harvested from the leg and used as a conduit to by-pass blood flow from the aorta to a point distal to an obstruction in a coronary artery. After a number of years, these grafts become diseased, and treatment of the graft is needed to improve blood flow. Treatment of these degenerated grafts with PTCA or Stenting is associated with a high incidence of embolic material (vessel deposits) released distally. This can result in a no-flow condition and myocardial infarction. Similarly, treatment of carotid arteries and renal arteries by PTCA and Stenting can cause release of embolic material. In the case of the carotid artery, emboli released can result in a stroke. In the case of the renal artery, emboli release can result in the renal infarct and reduced renal function. There is a risk of embolic material being released with any balloon expansion or passage of a treatment device through a diseased section of a vessel, with undesirable results to the patient. Thus, it is highly desirable to prevent embolic material from being released during treatment of vascular disease.
The use of embolic protection devices has recently improved the outcome for treatment of these diseased grafts and arterial restrictions. There are two major approaches to embolic protection. In either case the devices are delivered to the area of treatment in the conventional means through a guide catheter or elongated sheath.
The first approach involves crossing the obstruction or diseased vessel with a deflated balloon affixed to the distal end of a hollow guidewire. The balloon segment is placed distal to the arterial segment to be treated, and the balloon is inflated to occlude flow of blood in the vessel. The PTCA or Stenting treatment is then performed over the hollow wire and any embolic material is prevented from moving beyond the distal occlusion balloon. After completion of the treatment, a suction catheter is placed into the vessel such that the distal tip is near the balloon. Suction is applied to the catheter tip and embolic material is removed from the vessel.
The second approach involves a filter mounted on a guidewire and sheathed in a delivery catheter. The sheathed filter is placed in the artery distal to the treatment site. The filter is then deployed through the sheath and expands outward adjacent the vessel wall to channel blood flow into the filter. The treatment device is then advanced over the guidewire, and any emboli generated during treatment is directed by the blood flow into the filter. The filter retains embolic material greater in size than the filter pore size. After treatment, a recovery catheter is advanced distally to a location proximal to the filter and the filter pulled proximally. The filter closes and/or the filter is drawn completely into a lumen of the retrieval catheter. The system (and captured emboli) is then withdrawn from the body.
A balloon occlusion approach can be problematic because no blood is flowing through the vessel during use of the treatment device and ischemia can develop quickly, particularly in saphenous vein grafts. The procedure must be conducted swiftly to prevent undue patient pain. There is also no assurance that all trapped emboli are removed by suction.
A filter approach can be problematic because particles smaller than the filter pore size will pass through the filter and may cause embolic events or consequence, particularly in the brain. There is also no assurance that trapped emboli will not be squeezed through the filter mesh during recovery.
Recent clinical trials show that both types of embolic protection devices reduce the occurrence of embolic events by about half in the case of saphenous vein grafts. Clinical trials currently are assessing the benefit in carotid and other arterial treatments.
Unfortunately, these approaches to embolic protection do not eliminate embolic events entirely because passage of the protection device or the catheter delivering the device across the diseased section of the vessel or lesion can dislodge embolic material prior to deployment of the device. Thus, it would be highly desirable to use a device or method that would prevent release of embolic material during passage of the embolic protection system through the vessel lesion to the deployment location. One prior art attempt to solve this problem is disclosed in U.S. Pat. No. 6,348,062 (Hopkins et al.). In this approach a PTCA balloon is inflated proximal to the treatment site (lesion) to create stasis in the vessel. Emboli liberated on lesion crossing cannot be transported distally because there is no flow. A distal protection filter is then deployed and flow in the vessel is re-established. Any emboli created during lesion crossing by the distal protection device are prevented from flowing distally. The disadvantages of this system are that a treatment balloon must be advanced into the vessel prior to creating stasis, and advancement of this balloon may liberate emboli. Further, initial treatment with a balloon is not appropriate therapy for all procedures. For example, it may be more appropriate to initially debulk a vessel using atherectomy or thrombectomy by methods commonly used in the art. Finally, it is known that even passage of a guidewire can liberate emboli, especially in saphenous vein grafts. Placement of a balloon catheter requires pre-placement of a guidewire in this prior art approach.